1. Technical Field
The present invention relates to a method of fabricating semiconductor devices and, more particularly, to a method of forming a thin film for providing improved fabrication productivity.
2. Discussion of the Related Art
The fabrication of semiconductor devices involves many processes for forming various kinds of thin films. For example, a dielectric layer such as a silicon oxide layer (SiO2), a silicon nitride layer (SiN), a hafnium oxide layer (HfO2), an aluminum oxide layer (Al2O3), and the like is used for a gate oxide layer, an insulating spacer, an etch stop layer, a capacitor dielectric layer, and the like. Further, a conductive layer such as a polysilicon layer, a tungsten layer, an aluminum layer, or the like is formed for use in a gate electrode, interconnections, or the like. A chemical vapor deposition (CVD) method is widely used for forming the thin film, but the thin film formation process has recently focused on study of an atomic layer deposition (ALD) method. The ALD method forms thin films in the unit of an atomic layer, along with alternating chemisorption and surface reaction of reactant materials, and desorption of by-products, and it has many advantages such as an excellent step coverage and the like.
One of the problems associated with the thin film formation process is that an undesired thin film may be formed on the inner walls of a process chamber where the thin film formation process is being performed to form a process thin film on a semiconductor substrate. The thin film formed on the inner walls of the process chamber is peeled off from the inner walls of the process chamber as the thin films increase thickness, and the peeled films serve as particles which affect the thin film fabrication process, and provide one cause for reduction in production yield of semiconductor devices. Therefore, the thin film formation process also needs to include a cleaning process to remove periodically the undesired thin film deposited on the inner walls of the process chamber in order to prevent the above problem. In the conventional technology, a wet cleaning process is often employed to remove the deposited thin film from the inner walls of the process chamber by disassembling the process chamber and exposing it to an appropriate chemical solution. However, this wet cleaning process requires much down time, thereby causing a large loss in the production yield. Further, since the inside of the process chamber is exposed to the atmosphere, it may be contaminated by impurities in the atmosphere.
As one method of solving the above disadvantage of the wet cleaning processes, an in-situ cleaning may be employed, in which an etch gas is supplied into the process chamber without exposing the inside of the process chamber to the atmosphere, and the thin film deposited on the inner walls of the process chamber can be removed in situ state.
FIG. 1 is a flow chart illustrating a conventional method of forming thin films. Referring to FIG. 1, a semiconductor substrate is introduced into a process chamber (step 100). A process thin film is formed on the semiconductor substrate (step 102). During formation of the process thin film, a thin film is also formed on the inner walls of the process chamber. The semiconductor substrate is removed from the process chamber (step 104). Then, an in-situ cleaning is performed (step 106). The in-situ cleaning is carried out by supplying an etch gas into the process chamber, and etching the thin film deposited on the inner walls of the process chamber to remove it. In the conventional method, a plurality of semiconductor substrates can be sequentially treated inside the process chamber before performing the in-situ cleaning, while the number of the treated semiconductor substrates depends on the kinds and the thickness of the process thin films.
For high fabrication productivity, it is preferable to process a larger number of semiconductor substrates before performing the in-situ cleaning. However, if the number of semiconductor substrates that are treated before the in-situ cleaning is small, a process period of the in-situ cleaning is short, which is not preferable from the standpoint of productivity improvement. Further, in the conventional method as described above, if the thickness of the thin films formed on the inner walls of the process chamber is increased, since the thin film serves as particle source, there is a limit to the amount by which the period of the in-situ cleaning can be increased. Therefore, in order to improve the productivity of the thin film formation process, it is necessary to increase the period of the in-situ cleaning, and preferably, it is also necessary to shorten the process time required for the in-situ cleaning. In specific, the thin film formation process by the ALD method has characteristics in that a growth rate of the thin film is very low because of the formation of the thin film in the unit of atomic layer. Thus, a method of overcoming the above problem is further required in order to improve the productivity.
Furthermore, a method of forming an improved seasoning film on the inner walls of a process chamber to increase the cleaning period in the thin film formation process is disclosed in U.S. Pat. No. 6,589,868.